1. Field of the Invention
This invention relates to a crankcase emission control system or a crankcase ventilation system for an internal combustion engine.
2. Description of the Prior Art
In internal combustion engine, compressed air-fuel mixture and combustion products leak from combustion chambers into crankcase past piston rings. This leakage is called "blow-by gas". Since blow-by gases contain harmful components, it is necessary to prevent them from venting to the atmosphere.
A crankcase emission control system or a crankcase ventilation system returns blow-by gases back to combustion chambers in order to prevent their emission into the atmosphere.
TOYOTA COROLLA NEW MODEL MANUAL, on pages 7-77, issued by Toyota Jidosha Kogyo Kabushiki Kaisha on May 1983, discloses a crankcase ventilation system for a double-overhead camshaft (DOHC) engine having a pair of cam covers for inlet and outlet valve cam arrangements.
In this TOYOTA system, blow-by gas moves up from the crankcase into the cam covers and then travels to an intake manifold through a pipe. Only one of the two cam covers has an opening for venting the blow-by gas into the pipe, so that the covers differ from one another in shape. Therefore, it is necessary to use two different processes to manufacture the two cam covers. In addition, two cam chambers within the cam covers have different ventilation characteristics. Specifically, the ventilation characteristics of the cam chamber romote from the vent opening tend to be impaired.